1. Field of the Invention
The invention relates to a method of operating a washing machine using steam.
2. Description of the Related Art
The cleaning performance of a washing machine depends on many factors, such as chemical, mechanical, and thermal energy inputs during a wash cycle. The chemical energy relates to the detergent efficiency and water quality, the mechanical energy corresponds to fluid flow and fabric flexing and movement, and the thermal energy is associated with heating the wash liquid. However, a wash cycle that optimizes the chemical, mechanical, and thermal energy inputs to achieve superior performance does not necessarily correspond to efficient usage of natural resources, such as water and fossil fuels, including coal, oil, and natural gas. In view of rising resource costs and concern for environmental conservation, a practical balance between energy inputs and resource usage should be considered in the operation of washing machines.
One approach of reducing water consumption and power (i.e., natural gas or electricity) consumption has been to use steam rather than an immersion heater to heat the wash liquid. With an immersion heater, a larger volume of liquid than is needed for washing must be employed to maintain the heater completely submerged and thereby avoid damage to the surrounding structure. Furthermore, the heater must be powered for a relatively long period of time to heat all of the water required to submerge the heater.
Washing machines with steam generators can use less water than those with immersion heaters. Steam can be injected into the sump of the washing machine or directly into the tub or perforated drum rotatably mounted in the tub to heat the wash liquid. Although steam washing machines have been well-known for some time, methods of operating such washing machines to optimize cleaning performance and efficiently utilize natural resources are still needed.